Tiahleigh Palmer's foster brother denied bail

Queensland schoolgirl Tiahleigh Palmer may not have been the first underage girl her foster brother Trent Thorburn had a relationship with, a court has heard.

He has been in custody for about three months since being charged with having an incestuous relationship with the 12-year-old before her death in October 2015.

He is also alleged to have lied to secret Corruption and Crime Commission hearings investigating Tiahleigh's suspected murder.

The 19-year-old was denied bail in the Brisbane Supreme Court today on the grounds he could interfere with witnesses in the case and fail to appear at court in the future.

Justice John Bond said police were also concerned that Trent would reoffend if released from custody as they believed his alleged relationship with Tiahleigh was not the first occasion he had been with an underage girl.

Police allege Trent had sex with Tiahleigh at the family's Chambers Flats home, south of Brisbane, on or about September 26, 2015.

The court heard the revelation of their relationship was what allegedly instigated foster father Richard Thorburn to kill her a month later.